1. Field of the Invention
The present invention relates to a photo mask to be used for photolithography, and to a method of inspecting a pattern defect through use of the photo mask, and to a method of manufacturing a semiconductor device through use of the photo mask.
2. Description of the Background Art
Recently, demand has existed for an increase in the speed and capacity of a semiconductor device, and miniaturization of the device has also been pursued. Development of a system LSI formed from a combination of a semiconductor memory and a logic LSI has also been pursued in accordance with diversification of information processing.
So-called eDRAM (embedded DRAM) having DRAM and a logic LSI mixed therein is mentioned as one example of the system LSI. The eDRAM has the advantageous ability to process massive images at high speed.
FIG. 5 is a cross-sectional view for describing the structure of DRAM acting as a common semiconductor device. As shown in FIG. 5, reference numeral 101 designates a semiconductor substrate; 102 designates an element isolation region; 103 designates a gate insulation film; 104 designates a polysilicon film acting as a conductive film; 105 designates a tungsten silicide (WSi) film; 106 and 107 designate insulation films; 108 designates a side wall protective insulation film; and 109 and 115 designate poly-plugs which come into contact with a storage node. Reference numerals 110, 111, 113, 116, 117, 120 and 122 designate nitride or oxide films, which serve as interlayer dielectric films. Reference numerals 112 and 121 designate metal interconnections; 118 designates a storage node of a lower electrode; and 119 designates an upper electrode.
The semiconductor device (DRAM) such as that shown in FIG. 5 is manufactured by way of a plurality of manufacturing processes; that is, a film-growth process for forming a dielectric film and a conductive film; an etching process for forming a contact hole and a trench; a smoothing process using the CMP technique; and a photolithography process for forming a resist pattern.
Before and after each of the foregoing processes, a pattern defect inspection operation is performed for managing substances stuck to a product (product wafer). The pattern defect inspection operation is an inspection for specifying defective pattern attributable to extraneous matter, insufficient exposure, or etching failures, and is performed through use of an SEM (scanning electron microscope) or an optical microscope. Various types of inspection methods have been available in accordance with applications.
Next, a conventional photo mask to be used for photolithography processes will now be described.
FIG. 6 is a view for describing a conventional photo mask. FIG. 7A is a view for describing a conventional mask dimension inspection mark shown in FIG. 6.
As shown in FIGS. 6 and 7A, reference numeral 10 designates a photo mask; 2 designates a product pattern; 13 designates a mask dimension inspection mark; and 4 designates a line pattern.
The photo mask 10 shown in FIG. 6 is a reticle having drawn thereon a product pattern 2 and mask dimension inspection marks 13 provided on the periphery of the product pattern 2.
The product pattern 2 is a circuit pattern of an actual product.
The mask dimension inspection marks 13 are for measuring the processing precision of a photo mask at the time of production of the photo mask. Patterns of the mask dimension inspection marks 13 are originally unnecessary during the photolithography process. Hence, the patterns of the marks 13 are irrelevant to operation of the semiconductor device.
As shown in FIG. 7A, each of the mask dimension inspection marks 13 includes a plurality of line patterns 4 which are equal in width to that of the product pattern 2.
Next, a method of inspecting pattern defects (also called xe2x80x9cdefective patternesxe2x80x9d) using the conventional photo mask 10 will be described.
FIG. 7B is a cross-sectional view for describing a method of inspecting a pattern defect using a conventional photo mask.
As shown in FIG. 7B, a silicon nitride film 22 is formed to a thickness of about 500 angstroms on a semiconductor substrate 21, by the LPCVD method. Next, a silicon oxide film 23 is formed on the silicon nitride film 22 to a thickness of about 8,000 angstroms by the LPCVD method. Further, a photoresist film (not shown) is formed on the silicon oxide film 23.
Next, a wafer is exposed through use of a photo mask 10 shown in FIG. 6, thereby forming a resist pattern (not shown) on the silicon oxide film 23. Further, the wafer is subjected to dry etching while the resist pattern is used as a mask, whereby opening sections 28 corresponding to the mask dimension inspection marks 13 shown in FIG. 7A are formed in the silicon oxide film 23.
Subsequently, a barrier metal film 25 is formed from, for example, TIN or TaN, to a thickness of about 1,000 angstroms on the internal surface of each of the opening sections 28 and the silicon oxide film 23. Next, a tungsten film 26 is formed on the barrier metal film 25 to a thickness of about 4,000 angstroms, by means of sputtering. Further, unnecessary portions of the tungsten film 26 and barrier metal film 25 are removed from the silicon oxide film 23 by means of the CMP technique, whereby a structure such as that shown in FIG. 7B is produced.
Next, a product pattern (not shown), of the patterns formed in the manner as mentioned above, is subjected to a pattern defect inspection through use of an SEM or optical microscope. If defective patterns are found, the positions (coordinates) of defective patterns are specified while the patterns corresponding the mask dimension inspection marks 13 are taken as the points of origin (coordinate standards).
As mentioned above, utilizing mask dimension inspection marks 13 as coordinate standards when the coordinates of a defective pattern are specified during pattern defect inspection is effective for accurate specification of coordinates of the defective patterns.
However, the mask dimension inspection marks 13 are miniaturized for their originally-intended purposes in association with miniaturization of a semiconductor device and the product pattern 2.
Therefore, the mask dimension inspection marks 13 patterned onto a semiconductor substrate by use of the conventional photo mask 10 are difficult to find.
Particularly, since the mask dimension inspection marks 13 are miniaturized; namely, since the line patterns 4 are miniaturized, as shown in FIG. 7A, the opening sections 28 are completely embedded even when the tungsten film 26 is formed to a small extent, as shown in FIG. 7B. Further, if the wafer is smoothed by means of CMP after the formation of tungsten film 26, the surface of the wafer assumes a mirror state, thereby rendering the minute line patterns 4 much more difficult to find.
Therefore, at the time of pattern defect inspection, it is difficult to use the mask dimension inspection marks patterned onto the semiconductor substrate as coordinate standards. Hence, accurate specification of coordinates of a defective pattern cannot be carried out.
The present invention has been conceived to solve the previously-mentioned problems and a general object of the present invention is to provide a novel and useful photo mask to be used for photolithography, and is to provide a novel and useful method of inspecting a pattern defect, and is to provide a novel and useful method of manufacturing a semiconductor device.
A more specific object of the present invention is to perform inspecting operation of a pattern defect utilizing mask dimension inspection marks drawn on a photo mask.
The above object of the present invention is attained by a following photo mask to be used for photolithography, and by a following a method of inspecting a pattern defect, and by a following method of manufacturing a semiconductor device.
According to one aspect of the present invention, a photo mask to be used for photolithography comprises a product pattern; and a mask dimension inspection mark which is provided around the product pattern, the mask dimension inspection mark including a line pattern whose line width is equal to that of the product pattern, the mask dimension inspection mark including a reference pattern disposed adjacent to the line pattern, the reference pattern being a pattern of greater width than the line pattern.
Accordingly, the photo mask including the mask dimension inspection mark which can be used as coordinate standards for pattern defect inspection can be provided.
According to another aspect of the present invention, in a method of inspecting a pattern defect, a product pattern and a reference pattern are patterned on a semiconductor substrate by use of the above-mentioned photo mask. Next, a pattern defect is of the product pattern is inspected while the reference pattern is taken as a coordinate standard.
In the method of inspecting a pattern defect, a pattern defect inspection operation can be performed accurately by means of taking the mask dimension inspection marks as coordinate standards.
Further, since the pattern defect inspection operation can be performed accurately by means of taking the mask dimension inspection marks as coordinate standards, a highly-reliable semiconductor device can be manufactured.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.